REPRODUCTION BY GERM-CELLS 267 



' asexual reproduction,' since it groups together quite different things, 

 such as multiplication by single-celled and many-celled ' germs,' and is 

 moreover based on a quite erroneous idea of what ' fertilization ' really 

 is. Both terms may very well be retained as a mere matter of con- 

 venience, but it is much to be desired that the two apt designations 

 proposed by Haeckel — Monogony for asexual, and Amphigony for 

 sexual reproduction — should come into general use. 



Meanwhile it is enough to say that reproduction by 'spores' 

 occurs normally in Algae, fungi, mosses, and fern-like plants, and that 

 there are also animals in which the germ-cells possess the power of 

 giving rise of themselves to a new individual. But the cases which I 

 am chiefly thinking of are those of so-called virgin birth or partheno- 

 genesis, which are not to be compared with multiplication by spores 

 in regard to their mode of origin ; there is a peculiarity in the origin 

 of this mode of multiplication which I can only make clear after we 

 have studied the normal forms of what is called ' sexual reproduction.' 



We shall therefore pass on to this mode of reproduction. It is 

 well known that, in all higher animals, just as in Man, an individual 

 cannot reproduce by itself; the co-operation of two individuals is 

 necessary, and these — the male and the female — differ essentially 

 from each other in many particulars. Their union in the act of pro- 

 creation induces the development of a new individual, whether this 

 matures within the mother in a special receptacle, or whether it is 

 deposited as a ' fertilized egg,' as in birds, the lower vertebrates, and 

 most ' invertebrates.' 



As long as Man has lived he has regarded this process of 

 procreation as the essential factor in the origin of new individuals, 

 and as he had no insight into the essence of the process he had neces- 

 sarily to regard reproduction as something entirely mysterious, and the 

 co-operation of the two sexes as a conditio sine qua non of reproduc- 

 tion in general ; thus copulation and reproduction seemed identical. 



This was in the main the state of opinion at the time of the 

 discovery of innumerable minute filaments, the so-called ' spermatozoa ' 

 in the 'fertilizing' spermatic fluid of the male. The discovery was 

 made in 1677 by Leeuwenhoek in the case of birds, mammals, and 

 many other animals. Albrecht von Haller (1708-77) was at first 

 inclined to regard these spermatozoa as the rudiments of the embryo, 

 but later on, in the course of his long life, he withdrew this theory, 

 and declared them to be a kind of parasite in the spermatic fluid 

 without anything to do with fertilization. The same opinion was 

 expressed in" 1835 by K. E. von Baer, in opposition to the opinion 

 of Prevost and Dumas, who had rightly interpreted the spermatozoa 



